1. Field of the Invention
This invention relates to a method for producing a multicolor optical filter. Particularly, it relates to a method for producing a multicolor optical filter used in a color television-camera tube, a color solid state image sensor, etc.
2. Description of the Prior Art
Multicolor optical filters in the form of a multicolored stripe or a multicolored mosaic are used in color television-camera tubes or color solid state image sensors typified by charge coupled devices (CCD) or charge injection devices (CID). Usually, the multicolor optical filter is composed of three colors of: red, green and blue or cyan, magenta and yellow regularly aligned in a stripe or mosaic pattern. The color make-up is, however, not limited to these two 3-color combinations and the filter may be composed of two colors or four or more colors.
Conventionally known multicolor optical filters include dichroic mirrors as disclosed, for example, in Japanese Patent Publication No. 8590/65 and Japanese Patent Application (OPI) No. 3440/77 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application"), and dyed polymeric materials as disclosed, for example, in Japanese Patent Application (OPI) Nos. 37237/72, 63739/73 and 66853/73 and Japanese Patent Publication No. 248/78.
Manufacturing of these multicolor optical filters requires forming a photoresist corresponding to the pattern of each color, imagewise exposure wherein the mask must be precisely aligned, development, coloration or decoloration, removal of the resist, etc. Since these steps must be performed a number of times (usually, at least 3 times), the processes are very complicated and troublesome. Moreover, additional measures are required to obtain a superior multicolor optical filter. For example, when a multicolor optical filter is to be produced by repeating a process consisting of the formation of a relief pattern by coating a photoresist, imagewise exposure and development and coloration, care must be taken to ensure that a colored pattern formed in the coloration step in the previous process is not colored a different color in the subsequent processing. For this purpose a non-dyeing protective layer is sometimes applied at intervals between the coloring steps. As a result, the manufacturing becomes complex and the resulting multicolor optical filter becomes very expensive.
In order to overcome these defects, efforts have been made to use a silver halide color photographic material (a color film) in the optical filter manufacturing process. Such a process generally comprises exposing a coupler-incorporated color film or a color film adapted for development with a coupler-containing developer to light through a red, green and blue or a cyan, magenta and yellow master film, forming a color filter composed of cyan, magenta and yellow, or red, green and blue by photographic development using a coupler-free developer or a coupler-containing developer, bonding the color filter to a circuit glass plate, etc., for use as a faceplate of a television-camera tube, and further bonding the thin glass plate to the filter to produce the desired multicolor optical filter.
This method is described in detail by reference to FIG. 1 which shows the cross-section of a color film 10 composed of a minimum number of required layers. The color film 10 consists of a transparent base 11, a primer layer 12, a red-sensitive emulsion layer 13, an intermediate layer (anti-diffusion layer) 14, a green-sensitive emulsion layer 15, an intermediate layer (anti-diffusion layer) 16, a blue-sensitive emulsion layer 17 and a protective layer 18. Color films in actual use may include other layers or consist of the same layers arranged in different orders. Each of the emulsion layers has a thickness of about 5 .mu.m and each intermediate layer has a thickness of about 1 to 2 .mu.m. When this color film is exposed to red, green and blue lights (in the drawing, designated as R, G and B, respectively) as shown in FIG. 2 and processed, a cyan pattern 21 is formed in the red-sensitive layer, a magenta pattern 22 is formed in the green-sensitive layer, and a yellow pattern 23 is formed in the blue-sensitive layer, if the color film is of the coupler-incorporated type. As shown in FIG. 3, the color filter obtained is bonded to the surface of a circular glass plate 30 by an adhesive layer 31. A thin glass plate 33 is bonded to the color film 10 via an adhesive layer 32. Furthermore, a transparent electrode 34 and an optically conductive layer 35 are provided on the glass plate 33. Three color patterns 21, 22 and 23, such as those shown in FIG. 2, are formed on the color film 10.
In this manner, a faceplate of a color television-camera tube or a color solid state image sensor having the multicolor optical filter formed thereon is made. The above method, however, has the following defects. In commercially available color films, the size of the silver halide grains in the emulsions are considerably large, and the emulsion layer is of a multilayer structure having sensitivities to individual spectral wavelength regions. Hence, the resolving power of the color films is not so high. While it is expected that color films containing a Lippmann emulsion, which is a fine grain emulsion, would have some degree of high resolution, even if such a fine grain emulsion is used a complex multilayer arrangement of emulsion layers is required. Thus, the manufacturing process naturally becomes complex and expensive. Furthermore, as a result of the necessity of a complex multi-layered film structure, the resolving power of the resulting pattern is limited, and when a coupler-incorporated material is developed, the unreacted coupler remains in the emulsion layer and on standing for long periods of time the unreacted coupler is likely to color.